1. Field of the Invention
The invention generally relates to systems and methods for ozone generation and, more particularly, relates to an ozone generator having improved electrode design and configuration and improved voltage supply mechanisms, and provides improved ozone yields.
2. Description of the Related Art
Ozone (O.sub.3) is a naturally occurring compound in the atmosphere. Ozone may also be reactively generated by manmade systems and methods. To obtain reactively generated ozone, the dual atoms of oxygen (O.sub.2) are caused by electrical discharge to dissociate and to re-combine as three atom molecules, forming ozone (O.sub.3). The reactive formation of ozone is typically achieved utilizing what is known as a corona cell. A corona is a physical phenomenon characterized by a low-current electrical discharge across a gaseous gap at a voltage gradient exceeding a certain critical value. A corona cell is an apparatus that supplies such a corona. A typical corona cell configuration consists of two metallic electrodes separated by a gas-filled gap and a dielectric material.
In reactive formation of ozone via a corona cell, an oxygen-bearing gas flows through the discharge gap of the corona cell while high voltage is applied to the electrodes. The ozonation reaction is initiated when free, energetic electrons in the corona dissociate oxygen molecules: EQU e.sup.-1 +O.sub.2 .fwdarw.2O+e.sup.-1
Following this, ozone is formed by a three-body collision reaction: EQU O+O.sub.2 +M.fwdarw.O.sub.3 +M
Where M is any other molecule in the gas. At the same time, however, atomic oxygen and electrons also react with ozone to form oxygen: EQU O+O.sub.3 .fwdarw.2O.sub.2 EQU e.sup.-1 +O.sub.3 .fwdarw.O.sub.2 +O+e.sup.-1
Because all of these reactions take place when oxygen molecules are dissociated forming ozone, the net ozone that may be produced via a corona cell will depend upon the extent to which reaction variables are suitable to allow the reactions producing ozone to occur without significant destruction of the ozone produced because of the other reactions also occurring. In any case, the reaction variables and, thus, the ozone yield depend on many factors, including, for example, the oxygen content and temperature of the feed gas, contaminants in the feed gas, the ozone concentration achieved, the power density in the corona, the coolant temperature and flow, the effectiveness of the cooling system, and other factors. As may well be understood, these factors influence the design of ozone generation systems and methods, including design of corona cells for those systems and methods.
Ozone, both naturally occurring and that produced through reactive ozonation, is a gas with a penetrating odor. The gas is useful for many purposes. One particular use of ozone is in treatment of water to make it potable. An example of that use is described in U.S. patent application Ser. No. 08/214,644, titled TRANSPORTABLE, SELF-CONTAINED WATER PURIFICATION SYSTEM AND METHOD.
In producing ozone from oxygen, prior commercial ozone generators have used two basic corona cell geometries: concentric tubes and parallel flat plates. In those prior concentric tube type generator cells, the tubes serve as electrodes with a dielectric disposed therebetween in the annular space formed between the tubes. In the prior flat plate type generator cells, the dielectric is suspended between the flat plates maintained in a parallel arrangement. In the case of each type of prior corona cell design, an oxygen-bearing gas flows through the space between the electrodes, called the "discharge gap," while high voltage is applied to the electrodes. Electrically, a corona cell presents a capacitive load to the power supply due to both the gas-filled gap and the dielectric material present. As a direct result of power dissipation in the corona because of the discharge gap and dielectric, ozone is produced in the corona as oxygen and another gas are passed through the gap.
As can be understood, the various factors previously described as affecting net yields of ozone from an ozonation reaction are dependent, at least in part, upon the particular configuration of the corona cell of an ozone generator. One important characteristic of the corona cell configuration that dictates the factors is the physical characteristics of the discharge gap between the electrodes in which oxygen that is being dissociated to form the ozone flows. Another factor is the particular voltage gradient across the electrodes. Other factors include the particular characteristics of the electrodes, the dielectric, and the gases present in the cell.
Typically, trade-offs in design parameters of a corona cell for an ozone generator include distance between electrodes forming the discharge gap and voltages necessary to achieve an appropriate voltage gradient between electrodes. Generally, the wider the discharge gap, the higher the voltage must be and the greater the current necessary to sustain that higher voltage. Higher voltages in ozone generation can be problematic causing significant power of the ozone generator to be dissipated into heat, which heat destroys some or all of the ozone which is formed. Thus, to obtain optimum net yields of ozone from the ozonation reaction, it is advantageous to provide a narrower gap between electrodes, thereby requiring only lower voltages to achieve the necessary potential for the reaction. Of course, with lower voltages, lower currents may be employed and so less power will be dissipated into heat. The net effect, then, of a narrower discharge gap is that more ozone is obtained from the system because by utilizing lower voltages, and thus, lower currents, to achieve the ozonation reaction, less heat dissipation occurs and ozone produced through the ozonation reaction is not destroyed (at least not to the extent of destruction with higher voltages) after formation because of heat of the system.
The prior ozone generator systems and methods have attempted to reduce distance between electrodes forming the discharge gap in several ways. One approach has been to employ a shell and tube type arrangement, wherein the shell and tube form the electrodes and the dielectric in the annular space formed between shell and tube. This approach of the prior art has a number of disadvantages. For example, a disadvantage is that the tube of those arrangements has not been easily suspended in the shell in a manner which forms a uniform annular discharge gap. Another disadvantage has been that the suspension of the tube within the shell has required complex mechanical arrangements which have not made such a shell and tube arrangement easy to service and maintain. These are but a few of the disadvantages of the prior art.
The prior art ozone generator systems and methods have also sought to optimize ozonation by reducing system power that is dissipated as heat. As previously described, heat can destroy ozone and, thus, system power dissipated as heat is not desired. The prior art systems and methods have not effectively reduced system power dissipation for several reasons. Possibly the most significant reason is that the prior art shell and tube arrangements have not provided sufficiently insulated connections between internals of the shell and the power applied externally to the generator. Other disadvantages are also exhibited by the prior art.
Further, choice of materials has been an important disadvantage in the prior art because that has also been a reason for less than optimum ozone yields from those systems and methods. Prior art systems and methods have been limited with respect to materials available for use as electrodes and electrode material. The prior art has also been limited with respect to choice of insulative and connective materials.
The present invention provides significant improvement in the art and technology of ozone generation. As will be hereinafter more fully explained, the present invention overcomes many of the problems of the prior technology ozone generators. In particular, the present invention provides a reduced discharge gap width and, yet, maintains quite uniform discharge gap arrangement. The present invention also allows for ease of access for repair and maintenance of the electrodes and related corona cell mechanisms. Even further, the present invention provides significant improvement in insulation to reduce generator system power dissipated as heat, which reduction limits destruction of ozone formed. Finally, the present invention allows for advantageous selection of materials for achieving improved net ozone yields. As will be understood and appreciated by those skilled in the art, the invention is a significant improvement in the technology and provides the herein described advantages and improvements, and many others.